Department of Polar Sciences, University of Science and Technology, Incheon 21990, Republic of Korea.

Abstract

Inflammation triggered by the innate immune system is a strategy to protect organisms from the risk of environmental infection. However, it has recently become clear that inflammation can cause a variety of human diseases, including cancer. In this study, we investigated the effects of an ethanol extract of the Antarctic freshwater microalgae, Chloromonas reticulata (ETCH), on inflammation and carcinogenesis in RAW 264.7 macrophages and HCT116 human colon cancer cells, respectively. ETCH exhibited significant anti-inflammatory activity through the dose-dependent modulation of major inflammatory markers such as COX-2, IL-6, iNOS, TNF-α, and NO production. For example, ETCH reduced LPS-induced upregulation of COX-2, IL-6, iNOS, and TNF- alpha mRNA levels, leading to a significant decrease in the levels of LPS-stimulated NO and IL-6 as well as TNF-alpha products. In contract, ETCH exhibited dose-dependent cytotoxic activity against HCT116 cells, yielding a profound reduction in the proliferation of the cancer cells. Furthermore, ETCH induced G2 phase cell cycle arrest by transcriptionally regulating of genes involved in G2 / M transition including p21 (CDKN1A), cyclin B1 (CCNB1), and CDK1; CDKN1A mRNA levels were upregulated in response to ETCH, whereas CCNB1 and CDK1 were downregulated. This study reports for the first time anti-inflammatory and anti-cancer effects of, C. reticulata and provides new insights into the molecular mechanisms of the linkage between inflammation and cancer.

Effects of ETCH on cellular proliferation and NO production in LPS-induced RAW 264.7 macrophages. After 24 h of treatment, cell viability was evaluated using an MTT assay (A) and NO production was determined by Griess reaction (B). Statistical significance was determined by Student's t-test. The results are shown as mean ± SD values of three experiments. *p < 0.05, **p < 0.01, and #p < 0.001.

Effects of ETCH on the expression levels of proinflammatory regulators. The Transcriptional (A) and translational (B) expression levels of iNOS and COX-2 genes in response to ETCH treatment. The data have been normalized using an internal control, GAPDH. Statistical significance was determined by Student's t-test. Results are shown as mean ± SD values of three experiments; *p < 0.05, **p < 0.01, and #p < 0.001.

Effects of ETCH on the expression and production of proinflammatory cytokines. Transcriptional levels (A) and production (B) of cytokines, TNF-α and IL-6. Statistical significance was determined by Student's t-test. Results are shown as mean ± SD values of three experiments. *p < 0.05, **p < 0.01, and #p < 0.001.